An electric vehicle typically has an electric motor that is powered by a large capacity battery pack. The battery pack typically acts as a high voltage (e.g., 300-400V) direct current (dc) source. The electric motor is typically an alternating current motor. Accordingly, in order to drive the electric motor, the dc power from the battery pack is converted to alternating current or quasi-alternating voltage or current by an inverter. The inverter may be commercially provided in the form of a power module, comprising an array of power switches such as IGBTs, which form an inverter bridge as known in the art. The power module is typically commercially available in the form of a large isolated package (that may be, for example, about 200 mm×100 mm×30 mm) with several terminals for connecting to other electric drive components.
The power switches in the power module are switched at a relatively high frequency, e.g., 5 to 10 kHz or higher. At these frequencies, the inherent inductance of the system can cause large transient voltages to occur. These large transient voltages are undesirable because they can require the system designer to user more costly circuit components capable of handling high peak voltages. It is therefore desirable to reduce system inductance so as to avoid having to use such costly circuit components.
The system inductance includes several sources of inductance. One source of extraneous or stray inductance occurs in the power lines or bus bar used to couple the power module to other components of drive system.
For instance, in conventional high voltage electrical drive systems a large smoothing capacitor is typically connected across the inverter bridge. The smoothing capacitor is also typically commercially available in the form of an isolated package (which may be, for example, about 200 mm×70 mm×70 mm) with terminals for connecting to other components such as the power module. A bus bar may be used to connect the power module to the smoothing capacitor.
A conventional bus bar is a rigid high capacity conductor with terminals for connecting to terminals of other electrical components. Since the drive system is used in a vehicular application where the system may be subject to significant vibration during operation, the terminals of the various electrical drive components may be securely fastened together (e.g. using nuts and bolts that are fastened to one another with a selected torque) to prevent unintended consequences.
A conventional bus bar can carry significant stray inductance however, depending on its structure, size, the spacing between the positive and negative rails, and how well aligned the positive and negative rails are to one another. For example, a conventional bus bar assembly may have an inductance in the tens of microHenrys. The bus bar terminals and connecting structure in particular are a source for stray inductance since the structure of the bus bar is particularly non-uniform at the terminals and connecting structure.
It would be advantageous to provide a bus bar connector that provides reduced inductance as compared to some currently available bus bar connectors.